1. Field of the Invention
The present invention relates to a on/off control switch of a bi-directional motor.
2. Discussion of the Related Art
In many systems, for example in a car, a large number of motors are provided, each of which can be supplied with a dc. current having one polarity or the other to rotate according to one direction or the other. This is, for example, the case of the car window risers, all the motors of which are connected to the battery through an inverting element for connecting each motor according to one polarity or the other, a switch being associated with each motor to allow the powering of a single motor or of a plurality of motors simultaneously. Similar systems are provided for the locking of the doors or other locks in a car, for example the gas cap lock, for rear view mirror controlling devices, and so on . . . . Although the above examples are given in the case of a car, similar problems arise in other technological fields.
FIG. 1 is a simplified schematic diagram illustrating the aimed device. This device includes a plurality of motors M1, M2, M3 . . . respectively connected by a first terminal 11, 12, 13 . . . to the respective first terminals of respective switches S1, S2, S3 . . . . The second terminals 21 of the motors are common and connected to the common terminal of a first inverting element I1. The second terminals of the switches S1, S2, S3 are common and connected to the common terminal 31 of an inverting element I2. The inverting elements I1 and I2 can provide respective connections to a supply voltage, for example, a battery voltage, and to ground G, and the other way round. Thus, a current may flow in each motor according to one polarity or the other according to the positioning of the inverting arrangement I1-I2. Once the polarity of the current liable to flow in the motors is selected, one or a plurality of motors are powered depending upon whether one or a plurality of switches S1, S2, S3 are on. Thus, an individual control or a grouped control of the car windows, for example, can be achieved.
Conventionally, switches S1, S2, S3 are electromechanical switches. If it is desired to replace these electromechanical switches by static components, a first possibility is to use triacs TR1, TR2, TR3 . . . , as represented in FIG. 2, since the switches have to conduct a current in one direction or the other.
A first drawback to the use of triacs is presented by their control, because the common terminal 31 is either grounded or connected to voltage Vcc. For example, if it is desired to control the triacs through a microcontroller .mu.C connected between voltage Vcc and ground, the microcontroller will provide control signals referenced to ground. When common terminal 31 is grounded, the microcontroller can control a desired triac without problems. However, when terminal 31 is connected to voltage Vcc, a problem arises because the control signal cannot flow simply between the output of the microcontroller, which is near the ground voltage, and terminal 31, which is near voltage Vcc. A solution to this problem requires the provision, between the microcontroller output and the gates of the triacs, of a circuit or components allowing adjustment of the control signal.
FIG. 2 illustrates a possible structure of a passive adjustment circuit including three resistors and a capacitor for each triac based switch. The capacitor ensures an insulation between the voltage at terminal 31 and the microcontroller while allowing the transmission of pulse control signals. Other circuits based on active components (bipolar transistors) could also be provided. However, in all cases, the control of the switches is not direct and requires an interface to adjust the voltage of terminal 31.
A second drawback to the use of triacs is that they require a relatively high gate current and cannot, for example, be directly controlled by the outputs of a logic circuit or controller. A third drawback is that the various triacs TR1, TR2, TR3 . . . are necessarily realized on separate silicon chips because, at present, no means exists to integrate on the same chip triacs having a first common electrode, the common electrode being the electrode to which the gate is referenced.